The invention relates to composite roof structures and their preparation. The composite roof structures are prepared by adhering roofing material to a roof deck using a one-part, moisture curable, polyurethane adhesive composition containing dissolved or dispersed therein, reversibly blocked catalysts that are activated by moisture. Once activated by moisture the polyurethane adhesive composition foams in place. The adhesive compositions are storage stable in the absence of moisture and useful as a gap filling adhesive for adhering the roofing material to irregular surfaces.
In the roofing art many different methods are used to secure roofing materials to the roof deck structure, especially flat roofs. Mechanical fasteners have been used to secure roofing materials such as insulation boards and waterproofing membrane to the roof deck. However, the use of fasteners is undesirable because the method necessitates puncturing the roofing material and the roof deck. Even where the fasteners are coated with special materials to prevent corrosion and leakage, separation due to movement caused by thermal expansion and contraction, or wind uplift occurs thus compromising the effectiveness of the seal around the fastener. Additionally, when an old roof is replaced the old roofing material and mechanical fasteners are simply removed and new materials are laid down and attached with new fasteners. The numerous holes created by removing old fasteners weakens the integrity of the roof deck and creates routes of entry for water. In an effort to overcome the shortcomings of mechanical fasteners, methods to adhere roofing materials to the roof deck without mechanical fasteners have been developed. These methods typically utilize an adhesive composition in combination with the roofing materials and the roof deck to form a composite structure. U.S. Pat. No. 4,489,176 discloses the use of a polyurethane composition as a construction adhesive for applying insulation and decorative films on a number of substrates including roof decks. The polyurethane composition consists of a foam stabilizer, a prepolymer, a diluent, and optional auxiliary agents. The diluents used include the typical halogenated hydrocarbons well known as blowing agents in foam compositions. U.S. Pat. No. 4,996,812 describes a composite roof construction comprising a fleece-back flexible membrane, an adhesive, and the roof deck. The adhesive is preferably a foamed, cellular adhesive. The benefit of the invention resides in the use of the fleece-backed liner. The adhesive embedded in the fleece-back purportedly enhances the bond between the adhesive and the membrane and allows dissipation of the foaming gasses. U.S. Pat. No. 5,253,461 discloses a fastener free roof composite comprising a roof deck, insulation and an adhesive composition comprised of asphalt dispersed in an isocyanate prepolymer, with a compatibilizer. The adhesive may contain a non-reactive diluent. U.S. Pat. No. 5,872,203 discloses a two-part, moisture cure, polyurethane adhesive composition. The first part contains isocyanate or a prepolymer. The second part contains a polyether polyol, a reinforcing diol, a hydroxyl terminated polybutadiene and a tackifier. U.S. Pat. No. 5,895,536 discloses a method of adhering roofing tiles using a one-component adhesive. The method consists of applying a small amount of adhesive foam to each roofing tile rather than applying the adhesive as a bead or coating. No particular foam formulation is disclosed.
In many instances polyurethane has become the adhesive of choice in roofing applications. This is due in part to its well defined chemistry. Formulations of polyisocyanate terminated urethane prepolymers have successfully been used for both one and two-part polyurethane foam compositions. These foams may be used in aerosol form as described in U.S. Pat. No. 3,830,760 or when formulated with various quantities of foam stabilizers and low boiling diluents as described in U.S. Pat. No. 4,489,176 above. The disadvantages of two-part urethane foams as roofing adhesives are obvious. The two-part formulations require mixing and metering apparatus and cannot be combined until immediately prior to application. Disadvantages of conventional one-part, moisture curing, foamable, urethane adhesive formulations include their limited shelf life. One shelf life limiting factor is the dimerization of terminal isocyanate groups of the polyurethane prepolymer which is accelerated by catalysts contained in the formulation. This dimerization of the terminal isocyanate groups, even in tightly sealed containers free of oxygen and/or moisture, leads to discoloration of the prepolymer accompanied by increased viscosity. Further disadvantages associated with using conventional urethane foams whether one-part or two-part include environmental concerns over blowing agents, disposal of pressurized containers, and lack of fill capabilities of pre-foamed urethanes on irregular substrates.
The present invention provides an improved method of forming composite roof structures that addresses the problems found in the art. One-part, moisture curable, polyurethane adhesive compositions stabilized with a reversibly blocked catalyst, are used to adhere roofing materials to a roof deck. The stabilized polyurethane adhesive compositions are applied to the roof deck structure from unpressurized containers. Once exposed the compositions foam and cure rapidly, filing irregularities and providing bonds between roofing materials such as insulation board, fleece-backed elastomeric membranes, other polymeric roofing membranes, and the roof deck. The present invention eliminates the need for mechanical fasteners, bulky mixing and metering equipment, and pressurized product containers.